Home North pole ice How global warming causes both extreme heat and cold weather

How global warming causes both extreme heat and cold weather

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Texas guards help a motorist stranded in snow and ice on February 17, 2021 in Abilene, Texas. Photo: Texas Army National Guard / Staff Sgt. Yvonne ontiveros

It is evident that global warming can lead to record surface temperatures and heat waves. After all, there is “warming” in the term that describes the increase in global average temperatures due to the increase in greenhouse gases that trap heat and are emitted into the atmosphere. But the same process is also responsible for the record temperatures, which seems counterintuitive. A new study explains how global warming can lead to both sweltering heat waves and freezing blizzards by analyzing three extreme events from last winter.

Harsh winters and scorching summers: what’s the connection

On February 26, 2015, Senator James Inhofe (R-Okla.), Who was ironically enough the chairman of the Senate Environment and Public Works Committee, appeared with a snowball on the Senate floor to demonstrate, once and for all, that climate change is a hoax.

” You know what it is ? Asked Inhofe, the author of Biggest Hoax: How the Global Warming Conspiracy Threatens Your Future. “It’s a snowball from the outside here. So it’s very, very cold outside. Very out of season. Then he threw it on a congressional page.

This tasteless blow came at a time when it was very cold in the eastern United States. Since then, June 2021 has officially become the hottest June on record in North America, while July 2021 has been the worst for wildfires since the records began.

But while global warming and extreme cold may seem antithetical, they’re actually pretty well connected. And if Inhofe had been in good faith and listened to climate scientists, he would have known that too.

Research has linked the collapse of the polar vortex – a huge ring of cold, low-pressure winds in the Earth’s stratosphere above the North Pole – with extreme sub-zero temperature events. This is due to the polar vortex’s connection with the jet stream, a band of strong air currents flowing west to east about 10 kilometers above the surface. When the temperature rises sharply due to global warming, the interaction between the polar vortex and the jet stream can be significantly altered. The extreme weather conditions resulting from the interaction can be further magnified by changes in ocean temperature or sea ice in the Arctic Ocean.

Researchers led by Xiangdong Zhang, professor of climate and atmospheric sciences at the University of Alaska Fairbanks, showed this effect in action when they examined two record-breaking cold air outbreaks in China in late December 2020. to mid-January 2021. Meanwhile, the cities of Beijing and Tiajin experienced their lowest temperatures in 54 years at -19.7 ° C (-3.46 ° F) and -19.9 ° C (- 3.82 ° F), respectively.

Record-breaking cold weather in west-central and southern North America in February 2021 was also examined, which recorded the coldest temperatures on record in nearly a century in Texas and Austin, at -13 , 3 ° C (8 ° F) and -8.3 ° C (17 ° F), respectively.

Using observational data from the past 42 winters, the researchers integrated temperature readings into climate models that simulated the impact of marine and atmospheric events on extreme weather conditions.

“Even though global warming and the loss of arctic sea ice occur every year, the extreme weather events we study are intermittent – they don’t happen every year,” said co-author James Overland, research oceanographer at the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory in the United States “This is because they are caused by a combination of new global warming and extreme, but natural, precursor weather conditions in the jet stream and polar vortex. “

“The overriding problem to be resolved is why extreme weather events have occurred more frequently in a warming climate over the past decades and whether the amplification of arctic warming is playing a major driving role,” said Zhang added. “The extreme events of winter 2020-21 provide a unique opportunity to examine what physical processes or mechanisms drive these events. “

The results suggest that all three events were related to sudden stratospheric warming, although the downstream effects were different for each scenario. During East Asia’s first cold episode, polar air modulated the mid-latitude jet stream, directing cold air south. In the second case, the polar vortex split, deepening the region of low pressure bringing more cooler arctic air to the region. Finally, in North America, the polar vortex has also divided but this time the low pressure atmosphere has settled deeper to the south.

The study shows that atmospheric circulation and large-scale temperature anomalies can cause extreme weather conditions across the world, but due to slightly different factors. Satellite remote sensing can help validate these model simulations; and if so, scientists can use these models to better predict how precursor events influence the monsoon season in East Asia and other weather events. But anyway, the common denominator is global warming.

“By studying these record cold spells, we can see the ‘big picture’ of extreme weather events.” said co-author Zhe Han, a scientist at the Institute of Atmospheric Physics of the Chinese Academy of Sciences. “While the events may be different, they could share similar underlying mechanisms related to global warming. Along with warming, the amplification of the Arctic and the intensification of oceanic thermal anomalies can interact with atmospheric circulation, such as the polar vortex and sudden stratospheric warming, to cause extremely cold or hot events to appear.

The results were published in the journal Advances in atmospheric science.

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